1. Field of the Invention
The present invention relates to a bayonet type fixing device with which an annular member can be fixed to a cylindrical member. The present invention also relates to a zoom lens having the bayonet type fixing device.
2. Description of the Related Art
In a zoom lens, it is sometimes the case that an annular member is fixed to an annular end surface of another annular member so that the two annular members do not rotate relative to each other. For instance, according to a known fixing structure, a plurality of engaging projections formed on an annular ring are fitted in a corresponding plurality of engaging recesses formed on a cylindrical member, and subsequently a fixing ring (a retainer ring) is fixed to the cylindrical member with the annular ring being held between the fixing ring and the cylindrical member so that the annular ring can not come off the cylindrical member. The annular ring does not rotate relative to the cylindrical member due to the engagement of the plurality of engaging projections with the corresponding plurality of projections. According to such a fixing structure, when a large force is exerted on the annular ring in the axial direction thereof, especially in a direction that would cause the annular ring to disengage from the associated end surface of the cylindrical member, the annular ring, the fixing ring and/or a coupling portion between the cylindrical portion and the fixing ring may be damaged since such a large force has to be born by the annular ring and the fixing ring, which are generally small (thin) with respect to the optical axis direction.
The present invention has been devised in view of the above noted problem, and accordingly, an object of the present invention is to provide a bayonet type fixing device with which an annular member can be fixed to another annular member, and which excels in strength even though the structure of the fixing device is simple. The present invention also relates to a zoom lens having such a bayonet type fixing device.
To achieve the object mentioned above, according to an aspect of the present invention, a bayonet type fixing device includes a cylindrical member; an annular member attached to one end of the cylindrical member so as not to rotate relative to the cylindrical member; and a retainer ring attached to the cylindrical member to fix the annular member to the cylindrical member. The cylindrical member includes a plurality of engaging lugs formed at the one end of the cylindrical member to extend radially along a circumference of the cylindrical member; a plurality of insertion areas formed at the one end of the cylindrical member so that the insertion areas and the engaging lugs are alternately arranged along the circumference of the cylindrical member; a plurality of grooves formed behind the engaging lugs, to be connected to the insertion areas, respectively; and a plurality of recesses formed behind the grooves, to be connected with the grooves, respectively. The annular member includes a plurality of projections which are respectively fitted into the recesses via the insertion areas and the grooves. The retainer ring includes a plurality of engaging blades which are fitted into the grooves via the insertion areas to be positioned between the engaging lugs and the projections in an axial direction of the cylindrical member, respectively.
The projections can be respectively moved between the insertion areas and the grooves by rotating the annular member relative to the cylindrical member. The engaging blades can be respectively moved between the insertion areas and the grooves by rotating the retainer ring relative to the cylindrical member.
In an embodiment, a click-stop device is further provided which prevents the retainer ring from rotating in a direction of rotation that allows the retainer ring to come off one end of the cylindrical member after the retainer ring is properly engaged with the cylindrical member.
Preferably, the click-stop device includes a plurality of indentations respectively formed on the engaging blades of the retainer ring, and a plurality of corresponding notches formed on the cylindrical member to be respectively engaged with the indentations.
Preferably, the engaging lugs extend radially outwards, the projections extend radially inwards, and the engaging blades extend radially inwards.
Preferably, an external barrel is further provided, positioned around the one end of the cylindrical barrel to which the annular member and the retainer ring are attached, the external barrel being supported on the annular member.
In an embodiment, a plurality of inner guide grooves are formed on an inner peripheral surface of the external barrel so as to extend in an axial direction of the external barrel; the annular member includes a plurality of outer guide projections which extend radially outwards and respectively engage with the inner guide grooves of the external barrel; and the external barrel is guided in the axial direction so as to be movable with respect to the annular member via the inner guide grooves and the outer guide projections.
For example, the cylindrical member is a component of a zoom lens.
According to another aspect of the present invention, a zoom lens is provided, including a linear guide barrel guided in a direction of an optical axis; a rotational barrel coupled to the linear guide barrel to be rotatable relative to the linear guide barrel about the optical axis and to be immovable relative to the linear guide barrel in the direction of the optical axis; a plurality of lens groups guided in the direction of the optical axis without rotating about the optical axis via the linear guide barrel, the lens groups being driven in the direction of the optical axis in a predetermined manner in accordance with rotation of the rotational barrel; an annular member attached to a front end of the linear guide barrel so as not to rotate relative to the linear guide barrel; a retainer ring attached to the linear guide barrel to fix the annular member to the linear guide barrel; a plurality of engaging lugs formed at the front end of the linear guide barrel to extend radially along a circumference of the linear guide barrel; a plurality of insertion areas formed on the linear guide barrel at the front end thereof so that the insertion areas and the engaging lugs are alternately arranged along the circumference of the linear guide barrel; a plurality of grooves formed on the linear guide barrel behind the engaging lugs, to be connected to the insertion areas, respectively; a plurality of recesses formed on the linear guide barrel behind the grooves, to be connected with the grooves, respectively; a plurality of projections formed on the annular member, the projections being respectively fitted into the recesses via the insertion areas and the grooves; and a plurality of engaging blades formed on the retainer ring, the engaging blades being respectively fitted into the grooves via the insertion areas, to be respectively positioned between the engaging lugs and the projections in the direction of the optical axis.
Preferably, the projections are respectively moved between the insertion areas and the grooves by rotating the annular member relative to the linear guide barrel, and the engaging blades are respectively moved between the insertion areas and the grooves by rotating the retainer ring relative to the linear guide barrel.
In an embodiment, an external barrel is further provided, positioned around the annular member to be driven in the direction of the optical axis in a predetermined manner in accordance with the rotation of the rotational barrel. The external barrel is guided in the direction of the optical axis without rotating about the optical axis via the annular member.
Preferably, the annular member prevents the rotational barrel from moving forward in the direction of the optical axis relative to the linear guide barrel in a state where the annular member is fixed to the linear guide barrel via the retainer ring.
Preferably, the linear guide barrel includes a flange which prevents the rotational barrel from moving rearward in the direction of the optical axis relative to the linear guide barrel, the rotational barrel being held between the flange and the annular member.
Preferably, the flange is formed at a rear end of the linear guide barrel.
In an embodiment, the rotational barrel is a cam barrel having a plurality of cam grooves formed on an inner peripheral surface of the rotational barrel. The plurality of lens groups are driven in the direction of the optical axis in accordance with profiles of the plurality of cam grooves when the rotational barrel rotates about the optical axis.
Preferably, the rotational barrel is fitted on an outer peripheral surface of the linear guide barrel.
The above-described zoom lens can be incorporated in a digital camera.
The present disclosure relates to subject matter contained in Japanese Patent Applications No. 2000-23844 (filed on Feb. 1, 2000) which is expressly incorporated herein by reference in its entirety.